The review concluded that exercise training had beneficial effects on left ventricular modelling in clinically stable patients post myocardial infarction. Greatest benefits occurred when training started earlier after myocardial infarction (from one week) and lasted longer than three months. Low quality evidence and potential for bias mean that the authors' conclusions should be considered tentative.

Authors' objectives

To assess the overall effects of exercise training on left ventricular remodeling in clinically stable patients post myocardial infarction.

Randomised controlled trials (RCTs) that reported the effect of exercise training on ejection fraction and/or ventricular volumes in patients three months or less after myocardial infarction were eligible for inclusion in the review. Studies were excluded if they did not have a usual care control group or assessed the effects of exercise plus another intervention.

Participants in the included studies had impaired left ventricular systolic function (weighted mean ejection fraction 44%), a mean age of 55 years (range 46 to 69) and most (71% to 100%) were male. Ejection fraction was assessed by echocardiography, magnetic resonance imaging or radionuclide ventriculography. Most participants were on multiple medications. Outcomes included ejection fraction and end systolic and diastolic volumes. Time from myocardial infarction to the start of the exercise programme was six days to seven weeks. Exercise training was aerobic at 60% to 85% of baseline peak oxygen uptake (or heart rate) for 20 to 180 minutes a session three to seven times a week for one to six months.

Two reviewers independently selected studies for the review.

Assessment of study quality

Studies were assessed for quality using the Jadad scale. Reported criteria included description of randomisation procedures and blinding.

Two reviewers assessed studies for quality. Disagreements were resolved by consensus with a third reviewer.

Data extraction

Effect sizes for outcomes from each trial were calculated for each randomised group (experimental and control) and the difference between groups was estimated. Effect sizes were calculated as the difference between the mean outcome after the programme and prior to the programme, divided by the pooled standard deviation. The standard error of the mean effect size was calculated using meta-analysis and meta-regression methods by Lipsey and Wilson. Study authors were contacted to clarify data or provide additional data.

Two reviewers extracted data. Disagreements were resolved by consensus in discussion with a third reviewer.

Methods of synthesis

The authors planned to pool study data in meta-analyses. Substantial statistical, clinical and methodological heterogeneity meant that pooling of the study results was considered inappropriate. Meta-regression was performed to assess effects on ejection fraction, end systolic and diastolic volumes using two explanatory variables: time from myocardial infarction to initiation of exercise training programme and length of training programme.

Sensitivity analyses assessed the influence of excluding trials with a very short time (around one week) between myocardial infarction and initiation of the exercise programme.

Results of the review

Twelve studies (647 participants) were included in the review. Studies were considered low to moderate quality; none described randomisation procedures or blinding methods.

End systolic and diastolic volumes: There were greater reductions in end systolic and diastolic volumes when exercise training started early and lasted for longer.

The two variables of time from myocardial infarction and length of programme accounted for a significant proportion of between-study variation in outcomes (Q=25.5, p<0.01, R²=0.76 in 12 trials for ejection fraction, Q=23.9, p<0.05, R²=0.79 in nine trials for end systolic volume and Q=27.4, p<0.01, R²=0.83 in 10 trials for end diastolic volume). The trials were comparable when these variables were taken into account.

Sensitivity analyses did not markedly alter the direction of the findings.

Authors' conclusions

Exercise training had beneficial effects on left ventricular modelling in clinically stable patients post myocardial infarction. Greatest benefits occurred when training started sooner after myocardial infarction (from one week) and lasted longer than three months.

CRD commentary

The review addressed a clear research question supported by appropriate inclusion criteria. A wide range of relevant sources were searched for studies. Only published studies in English were included and language and publication bias could not be ruled out. Appropriate methods were used to select studies, extract data and assess study quality, which minimised risks of reviewer error and bias. An appropriate tool was used to assess studies for quality. Studies were mostly of low to moderate quality and this may have influenced the reliability of the conclusions.

The authors' decision not to pool studies was appropriate given the high levels of statistical, clinical and methodological heterogeneity between the studies. Different times from myocardial infarction to initiation of treatment and duration of treatment were significantly associated with differences in effect sizes for the outcomes and significantly explained heterogeneity in the outcomes. Other potential effect modifiers (type and location of infarction) were not analysed because of insufficient information. Sensitivity analyses supported the overall findings.

Low quality evidence and potential for bias mean that the authors' conclusions should be considered tentative.

Implications of the review for practice and research

Practice: The authors stated that following uncomplicated myocardial infarction clinically stable patients should begin aerobic exercise training from one week after hospital discharge and continue training for up to six months; this represented a significant change in practice.

Research: The authors stated a need for further high quality RCTs of the effect on left ventricular remodelling of exercise soon after myocardial infarction. Future trials should include more women and should measure and assess the specific effects of type/location of infarction and exercise capacity.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.